This invention relates to a technique for preventing unauthorized copying of an analog television signal by a digital video tape recorder (VTR), and more particularly to such a technique in which a scrambled signal is recorded when copying of an analog input signal is not authorized.
There has been proposed a VTR for consumer use in which program information in the form of a video signal and an associated audio signal are recorded in digital form on a magnetic tape. Digital recording of video signals and associated audio signals makes it possible for such program information to be reproduced and copied (or "dubbed") onto another tape with little or no deterioration in the quality of the signal reproduced from the copy tape. There are times, however, when it is desirable to prevent such signals from being recorded. For example, in order to protect the rights of those holding a copyright in the recorded material, copyright protection schemes have been proposed in which the digital recording format includes copyright protection information recorded in auxiliary information recording areas on the same magnetic tape with the program information. Such proposed copy protection systems are designed to prevent unauthorized copying of a signal that is transmitted in digital form from one digital VTR to another. In particular, when a digital signal reproduced from the magnetic tape is supplied as an input signal for recording to a VTR, the operation of the recording circuitry in the digital VTR is either permitted or inhibited in accordance with the copy protection information that is included in the input digital video signal. Thus, if the information indicates that the program information is not available for copying, the recording circuitry is controlled either to completely prevent any recording, or so that a scrambled video signal is recorded on the tape.
A similar copyright protection system relating to digital audio tape recordings is disclosed, for example, in U.S. Pat. Nos. 5,057,947 and 5,185,792, in which it has been proposed to provide within the copyright protection information a bit which indicates the "generation" of the tape on which digital audio data has been recorded. For example, the "generation" bit, may indicate either that the tape is an "original" recording, or that it is a copy of an original recording.
With respect to digital VTRs that can provide analog video and audio output and can receive analog video and audio signals as input signals, transmission of the video and audio signals in analog form from one digital VTR to another permits the receiving VTR to record a very high quality signal in digital form. The previously proposed copy protection systems for digital VTRs are, for the most part, directed to prevention of copying of a digital input signal, and therefore are not effective to prevent a digital VTR from recording a signal received in analog form, and the high quality of the resulting copies makes such copies a significant threat to the interests of those owning rights in the program information, such as copyright holders.
Moreover, there are a number of other sources of protectable program information in the form of video signals besides analog or digital video outputs from digital VTRs. Among these are television program signals broadcast from conventional terrestrial stations, television programs broadcast from satellites, video signals output from video disc players, television programming distributed by cable, and pay-per-view programming distributed by satellite or by cable. In some cases the broadcast signal may be free of any copyright but in other cases copyright is asserted. It is desirable that copying of the signals be prevented when a copyright is asserted with respect to the material represented by the signal or when the owner of such program information wishes to prevent unauthorized copying thereof.
Reference is made to co-pending patent applications Ser. Nos. 08/220,049, filed Mar. 30, 1994 and 08/094,433, filed Jul. 21, 1993, each of which has a common inventor and a common assignee with this application, and in which further details of video signal copyright protection systems are disclosed.